Guidance system for laser targets

ABSTRACT

A system for guiding charged laser targets to a predetermined focal spot of a laser along generally arbitrary, and especially horizontal, directions which comprises a series of electrostatic sensors which provide inputs to a computer for real time calculation of position, velocity, and direction of the target along an initial injection trajectory, and a set of electrostatic deflection means, energized according to a calculated output of said computer, to change the target trajectory to intercept the focal spot of the laser which is triggered so as to illuminate the target of the focal spot.

BACKGROUND OF THE INVENTION

The invention described herein was made in the course of, or under,Contract No. W-7405-Eng-48, with the United States Energy Research andDevelopment Administration.

The invention relates to guidance systems, particularly to guidancesystems for laser targets, and more particularly to a guidance systemfor charged lser targets for directing such targets to a focal spotwithin a conrolled thermonuclear reactor for illumination by a laser.

Guidance systems for ion beams, droplets, and pellets, etc., are knownin the art as evidenced by U.S. Pat. No. 3,582,958 issued June 1, 1971in the name of C. D. Hendricks, Jr., and U.S. Pat. No. 3,723,246 issuedMar. 27, 1973 in the name of M. J. Lubin; an article entitled"Collision, Coalescence, and Distruption of Water Droplets" by J. R.Adam et al., Journal of Applied Physics, Vol. 39, No. 11,5173-5180,October 1968; and an article entitled "Laser-Induced ThermonuclearFusion" by J. Nuckolls et al, Physics Today, August, 1973. The abovereferenced prior known guidance systems are of the electrostatic typewhich utilize electrodes functioning as deflection plates to direct theflight path of the material concerned. In controlled thermonuclearreactor (CTR) system, there is a particular requirement for aneffective, accurate target guidance system to insure that each of thetargets, which for example may be injected at the rate of 100 per sec.,is directed through the focal spot of the laser beam. Therefore, thereis a need in the CTR field for a guidance system which can reproduciblydeliver targets or pellets to the laser focal spot at predeterminedinstants of time.

SUMMARY OF THE INVENTION

The present invention is a guidance system for reproducibly deliveringlaser targets injected into a CTR to a focal spot of the laser beam. Theguidance system is particularly adapted for guiding such targets along ahorizontal injection trajectory, but may also be utilized in vertical ortangential target injection modes. Broadly, the guidance systemcomprises a first series of electrostatic sensors which provide inputsto a computer for real time calculation of position, velocity, anddirection of the target along an initial injection trajectory, and a setof electrostatic deflection means energized according to a calculatedoutput of the computer to change the target trajectory to intercept thefocal spot.

Therefore, it is an object of this invention to provide a guidancesystem for laser targets.

A further object of the invention is to provide a system for guidingcharged laser target along a trajectory to intercept the focal spot of alaser.

Another object of the invention is to provide a guidance system forlaser targets wherein a computer provides real time position, velocityand direction information of the target injection trajectory forcontrolling target deflection means to assure reproducible delivery ofthe target to the laser focal spot.

Another object of the invention is to provide a guidance system forcharged laser targets injected along a horizontal direction forreproducibly directing the trajectory of such targets to intercept thefocal spot of a laser.

Another object of the invention is to provide a guidance system forcontrolling the trajectory of laser targets injected into a CTR so thatsuch targets intercept the focal spot of a laser for illuminating thetargets.

Another object of the invention is to provide a guidance system forcharged laser targets injected into a CTR wherein electrostatic sensorsprovides inputs to a computer for real time calculation of position,velocity, and direction of the target along an initial injectiontrajectory, and electrostatic deflection means energized according tothe calculated output of the computer controls the target trajectory soas to intercept the focal spot of a target illuminating laser.

Other objects of the invention will become readily apparent to thoseskilled in the art from the following description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The single FIGURE schematically illustrates an embodiment of a lasertarget guidance system made in accordance with the invention.

DESCRIPTION OF THE INVENTION

The invention is directed to a guidance system for laser targets orpellets injected into a Cont. Ther. Reac. (CTR) to control thetrajectory of the targets such that they pass through the focal spot ofa laser system triggered to illuminate, vaporize, ionize, or implode thetarget by laser energy.

While the invention is applicable to vertical, tangential, andhorizontal target injection techniques in magnetic confinement and laserfusion CTR systems, the invention is described hereinafter for guidingthe trajectory of charged laser targets along a horizontal direction ina magnetic confinement CTR, such as that known as the Baseball IIfacility, but it is not intended to limit the invention to any specifictype of system.

The laser targets may constitute pellets produced using the fluid jetprocess described in an article by J. M. Schneider, et al., Rev. Sci.Inst. 35, 1349, 1964 or they may be composed of charged frozen ammoniapellets, for example, wherein the charged pellets are directed through asmall, shaped orifice to a high vacuum (about 10⁻⁵ torr) region wherethey freeze by evacuation such pellets or targets being produced in atarget generating system described and claimed in copending U.S. patentapplication Ser. No. 698,557 filed June 22, 1976 in the name of R. K.Goodman et al. The thus generated targets are guided from the targetgenerating system along a generally horizontal trajectory into themagnet confinement region of a CTR by the guidance system to control thetarget trajectory to insure reproducible delivery of the targets to thefocal point or spot of a laser system. As shown in the drawing, acharged target 10, composed for example of ammonia impregnated with anelctrically conductive material such as HCL, is ejected from a targetgenerating machanism indicated at 11 along an initial horizontaltrajectory 12 which passes through the guidance system composedgenerally of a sensor section 13, a micro processor or computer 14, avoltage amplifier 15, and a deflection section 16, along a finaltrajectory 17 to a focal point or spot 18 within a magnetic confinementregion or target zone 19 or a lens 20 to be illuminated by a laser beam21 passing through the containment wall of the CTR from a laser system22, where in this embodiment the target 10 is vaporized and ionized bythe laser energy of beam 21 to generate a target plasma which is usedfor trapping a beam of energetic neutral particles. Inasmuch as thedetails of the target generator 11 and the CTR and laser system 22 donot constitute part of this invention, and since exemplary embodimentthereof are known in the art as illustrated by the above cited priorart, detail description thereof is deemed unnecessary.

The components generally indicated at 13-16 constitute an embodiment ofthe target guidance system of this invention. Sensor section 13comprises a first set of electrostatic sensing plates 23, an annularsensor 24, and a second set of electrostatic plates 25, each generatingoutput signals 26, 27 and 28, respectively, which are directed intomicro processor 14. The first set of sensing plates 23 (four plates)sense a time of arrival t_(o) and initial x and y coordinates (x_(o)-y_(o)) of the trajectory 12 of target 10. The annular sensor 24positioned at a distance d, from plates 23 establishes the time t', atwhich the target 10 passes, permitting calculation of the targetvelocity. The second set of sensing plates 25 furnish a secondmeasurement of x and y coordinates (x₁ -y₁) at a known distance d₂ fromthe first point of coordinate measurement (plates 23) which defines thespacial parameters of the trajectory 12. Taking a measurement of a time,t', prior to the second coordinate measurement from sensing plates 25enables more effective use of computer time, which is critical in viewof the limited target transit time. The time, t', is taken by theannular detector 24. For example, distance d, is 8cm and distance d₂ is40cm, and a typical time frame from t_(o) to t' is 2.67 msec, with thetarget velocity being about 30 meters/sec. The signals 26, 27 and 28provide inputs to the micro processor or computer 14 for real timecalculation of position, velocity, and direction of the target 10 alongits initial injection trajectory 12, which enables the micro processor14 to then calculate and issue via voltage amplifier 15 the necessarysignals to appropriately power the deflection section 16 to bring thetarget on final trajectory 17 leading to the laser focal point 18.

The details of the micro processor or computer 14 do not constitute partof this invention but generally is composed of a signal processingsection which digitizes the incoming signals 26, 27, and 28, a memorysection in which the digitized signals are stored and an INTEL model8080 chip which forms the heart of the computer section.

Voltage amplifier 15 may be of a conventional type capable of receivinginput signals 29 from micro processor 14 in the range of 0 to 10 andamplifying such signal to the 0 to -5Kv range and dividing the outputthereof into signals 30 and 31 which are directed to deflection section16.

Deflection section 16 comprises two pairs of deflection plates 32 and33, pair 33 being positioned at 90° with respect to pair 32 andconnected to received output signal 30 and 31, respectively, fromvoltage amplifier 15. The pairs of deflection plates 32 and 33 arepositioned at a sufficient distance d₃ from sensing plates 25 to allowsufficient time for the micro processor 14 to process the sensing signal26-28 and calculate course correction signals which are amplified at 15and impressed upon deflection plates 32 and 33 to appropriatelyestablish the final trajectory 17 of target 10. For example, thedistance d₃ is 44 cm with a time of about 15 msec, while the distance d₄from the deflector plates to the focal point 18 is about 1.2 meters witha time of about 40 msec.

Tests conducted on the above described guidance system using chargedammonia targets or pellets have shown that the system provides effectivemeans for accurately guiding charged laser targets to a predeterminedfocal point or spot along generally arbitrary, and especiallyhorizontal, directions, thereby providing a practical guidance systemfor charged targets, thus substantially advancing the state of the artin this field.

As pointed out above, while the guidance system has been described andillustrated for horizontal injection applications in a magneticconfinement CTR field, it can be effectively utilized in the laserfusion CTR field, as well as having applications to the vertical andtangential target injection techniques.

While a particular embodiment, parameters, etc., have been illustratedand/or described, modifications and changes will become apparent tothose skilled in the art, and it is intended to cover in the appendedclaims all such modifications and changes that come within the scope andspirit of the invention.

What we claim is:
 1. A guidance system for targets comprising;electrostatic sensing means for generating signals responsive to x and ycoordinates and time of travel of an associated target over apredetermined distance along an initial trajectory, micro processingmeans for receiving said signals from said sensing means for real timecalculation of position, velocity, and direction of such an associatedtarget and for producing calculated course correction output signals,electrostatic deflecting means positioned in alignment with said sensingmeans and responsive to said calculated course correction output signalsfrom said micro processing means for correcting the trajectory of suchan associated target, and amplifier means operatively connected betweensaid micro processing means and said deflecting means for amplifyingsaid calculated course correction output signals.
 2. The guidance systemdefined in claim 1, wherein said sensing means comprises a first set ofplates which sense a time of arrival and initial x and y coordinates ofan associated target along the initial trajectory, an annular sensoraligned with and spaced from said set of plates which establishes thetime at which such an associated target passes thereby, and a second setof plates aligned with and spaced from said annular sensor which sense xand y coordinates at a predetermined distance from said first set ofplates.
 3. The guidance system defined in claim 1, wherein saiddeflecting means comprises at least two pairs of spaced deflectionplates, one pair of plates being oriented about 90° with respect to theother pair of plates, said pairs of deflection plates being aligned withand spaced from said sensing means to allow sufficient time for saidmicro processing means to process said signals from said sensing meansand calculate said course correction signals, each of said pairs ofdeflection plates being operatively connected to said amplifier meansfor receiving output signals therefrom.
 4. The guidance system definedin claim 2, wherein said deflecting means comprises two pair of spaceddeflection plates with one pair positioned about 90° with respect to theother pair, said pairs of deflection plates being aligned with andspaced from said second set of plates of said sensing means, each pairof said deflection plates being operatively connected to said amplifiermeans for receiving said calculated course correction output signals.